Chloro-p-phenylene diamine and related diamines are unstable to storage The compounds that form on storage of chloro-p-phenylene diamine, even in sealed containers, are discolored and without repurification, the stored product is likely to provide polyamides of reduced molecular weight on polymerization with, for example, terephthaloyl chloride. As is well known, low molecular weight polymer commonly results in fiber with poorer tensile properties.
Chloro-p-phenylene diamine is also unstable at high temperatures and this creates particular difficulties in its purification. By contrast, the hydrochloride salts of chloro-p-phenylene diamine and its analogs have much superior stability to the free diamine.